1. Field of the Invention
This invention relates to explosion vents adapted to be mounted vertically or horizontally, or at an angle from vertical or horizontal, and disposed in closing relationship to relief openings in enclosed areas subject to rapid overpressure conditions such as may occur during explosions, a fast burning fire, or the like. Various industrial processes and installations have confined particulate materials, gases, and/or finely divided fluids that can explode or ignite creating a significant explosion or fire. Dangerous overpressure conditions can result from an explosion or an uncontrolled fire. It is therefore desirable to protect areas that confine hazardous materials subject to rapid combustion from what would otherwise be a catastrophic explosion or fire.
More particularly, this invention relates to full opening and reclosable explosion vent apparatus that will consistently open when the area protected by the vent is subjected to a pressure buildup of a predetermined magnitude, without premature opening of the vent when an overpressure condition occurs that is below the set opening pressure of the vent. The explosion vent apparatus is constructed and designed to withstand continuous pressure cycling over an extended period of time below the pressure that effects opening of the vent without adversely affecting the pressure relieving characteristics of the vent.
The vent panel of the vent apparatus of this invention is openable to a first pressure relieving partially open position, without rupture of the vent panel of the apparatus, when subjected to an overpressure condition of one magnitude, and openable to a second fully open pressure relieving position, again without rupture of the vent panel, when the vent panel is subjected to an overpressure condition of a higher magnitude. An especially important advantage of the explosion vent apparatus is its ability to reclose from either of its open positions when the overpressure condition is relieved, thus preventing ambient air from reentering the opening leading to the protected area that could cause a secondary explosion or increase the intensity of a fire. Reclosing of the vent is accomplished either with a pneumatic apparatus, torsion springs, or elastomeric bands.
2. Description of the Prior Art
Explosion vents are commonly used to cover relief openings in enclosures such as bag houses, filter installations, dryer systems, tanks, processing vessels, and conduit systems for preventing dangerous overpressure conditions in such restricted areas. For example, bag houses, filter installations, and dryer systems are constantly at risk of explosions because of the high concentrations of finely divided materials, gases, and fluids that may be present. In order to protect these hazardous areas from damage caused by an explosion or a fast reacting fire that creates an extremely rapid overpressure condition, it is conventional practice to provide one or more pressure relief openings in the equipment that seal the protected area from the surroundings outside the protected area. These explosion vents seal the pressure relief openings when the equipment or systems operate at normal pressures within prescribed limits. When the confined areas are subjected to an overpressure condition of predetermined magnitude, each vent normally closing a pressure relief opening ruptures or bursts allowing the high pressure matter to escape through the relief opening. Explosion vents have been designed to consistently burst at a particular pressure level, substantially regardless of the number of pressure cycles that the vent has been subjected to over a period of time.
Areas containing materials that present an explosion or fast reacting fire producing a rapid overpressure condition are also frequently subjected to vacuum conditions. Consequently, prior vent panels designed to burst when an overpressure of predetermined magnitude occurs, must also be capable of withstanding a certain vacuum without failure. Additionally, bag houses and filter installations, for example, are often cycled between pressuring vacuum conditions, causing the explosion vents to flex back and forth. One common practice is to direct pulses of air against the face of a bag house filter which collects dust particles thereon, to dislodge the particles from the surface of the filter so that the particles fall to a collection area below the filter bags. Thus, explosion vents must be configured to withstand or resist vacuum pressures and cycling between pressure and vacuum conditions without collapsing inwardly into the protected area.
Prior art explosion vents typically have been provided with a relatively thin flat metal sheet with the edges trapped between opposed frame members. The vent panel itself has been supplied in a number of different embodiments, with the material of construction, thickness of the material, and a variety of features such as lines of weakness defined by slits or scores, or the configuration of the lines of weakness, controlling the burst pressure. In all instances, though, pressure relief is accomplished by rupturing or breaking of the vent panel, usually along the lines of weakness if provided.
Certain prior art explosion vents having slits defining a line of weakness have been provided with a plurality of connectors or burst tabs attached over the slits to retain the central area of the panel within the confines of the line of weakness in its closed position until subjected to a buildup of pressure of predetermined magnitude. With this burst tab construction, it was difficult to assure bursting or rupture of the vent panel at a prescribed overpressure level because the burst tabs were not all subjected to uniform forces, causing some of the burst tabs to break prematurely. It is to be recognized in this respect that when one or more of the burst tabs break prematurely, the remaining burst tabs break in an indeterminate successive order. Providing an additional number of these burst tabs has not proved successful because the vent panel then tends to rupture late and not provide adequate protection from an explosion or incipient fire.
The provision of tabs across a line of slits also have limited the vacuum support properties of vent panels because it has been found difficult to provide tabs that offer sufficient resistance to inward buckling of the panel, while at the same time being capable of controlling outward rupture of the vent at a pressure of predetermined positive magnitude. In high vacuum conditions, it has been necessary in certain instances to provide reinforcement for the vent panel which complicates the forward acting burst properties of the panel, and at the same time increases the complexity, weight, and cost of the panel assembly.